Category: Linux and UNIX

The UNIX Operating System has a long and influential history in computing and Brian Kernighan’s new book, UNIX: A History and a Memoir tells that story. I started teaching UNIX (and C programming) for Learning Tree back in 1984. A lot has changed since then including the advent of Linux, the move to PCs, and […]

As you may know, there are two kinds of email systems: Outlook, and everything else. The non-Outlook-based email world consists mainly of three kinds of software: MDAs, MUAs, and anti-spam/antivirus. Dovecot is the glue between your MDA and your MUA.[gview file=”https://blog.learningtree.com/wp-content/uploads/pdf/dovecot-email-flow.pdf”] MDAs are the mail delivery agents, such as SendMail, PostFix, OpenSMTPD, and more. An […]

In this blog I described some of the logical problems with vulnerability scanners. False positive and false negative errors. Additionally, the worry that problems exist but our tool hasn’t even tried looking for them. Let’s try to make this practical! I’m working on a consulting job as a sub-sub-contractor on a U.S. Department of Defense […]

Many of you must follow formal cybersecurity requirements. PCI DSS, if you accept credit or debit cards. HIPAA, if you store or process health care data. Then, if you’re with the Department of Defense or other U.S. Government agencies, there are more detailed configuration requirements. In theory, you could just read the requirements and then […]

While it may seem strange, sometimes it is possible for a mathematical expression to have two different right answers. Consider: This expression has been discussed on the Internet since 2011! The correct answer could be either 2 or 288. Really. It depends on how the expression is evaluated. To understand that we have to understand […]